1. Field of the Invention
The present invention relates to a high pressure pump.
2. Description of Related Art
A high pressure pump, which supplies fuel to a fuel supply system of an internal combustion engine, is known. Fuel, which is drawn out of a fuel tank, is supplied into a pressurizing chamber upon downward movement of a plunger in a cylinder hole of the high pressure pump. Then, the fuel is metered and is pressurized in the pressurizing chamber upon upward movement of the plunger in the cylinder hole.
At a process of assembling such a high pressure pump or at a process of installing the assembled high pressure pump to the engine, it is required to limit falling off of the plunger from the cylinder hole.
In a high pressure fuel pump recited in JP2008-525713A or a fuel pump recited in JPH04-231673A (corresponding to U.S. Pat. No. 5,174,734), a countermeasure is taken to limit the falling off of the plunger from the cylinder hole. For example, in the high pressure fuel pump of JP2008-525713A, a step portion of a piston (plunger), which is received in a casing, cooperates with a stopper of a stopper element fixed to the casing.
Furthermore, in the fuel pump of JPH04-231673A (corresponding to U.S. Pat. No. 5,174,734), a range of outward movement of a plunger is limited by a circlip, which is engaged with tongues. In this way, during transportation of the fuel pump or assembling of the fuel pump to the engine, it is possible to limit the falling off of the plunger from the cylinder hole (bore).
However, in the high pressure fuel pump of JP2008-525713A, when the step portion, which is formed between a large diameter portion and a small diameter portion of the piston, contacts the stopper of the stopper element, a portion of an outer peripheral wall surface, i.e., a slide surface of the large diameter portion of the piston, which slides along an inner peripheral wall surface of a piston bush, is exposed from the piston bush.
Therefore, when the step portion of the piston contacts the stopper, the exposed slide surface of the piston may possibly be damaged by hitting with another object to cause deformation of the slide surface of the piston. Furthermore, a foreign object (e.g., debris) may possibly adhere to the exposed slide surface of the piston. In both of these situations, slide malfunction of the piston may possibly occur.
In the fuel pump of JPH04-231673A (corresponding to U.S. Pat. No. 5,174,734), the circlip, which limits the range of the outward movement of the plunger, is placed at a location, which is spaced from a body part that forms the cylinder hole (bore). When the plunger contacts the circlip, a portion of the outer peripheral wall surface of the plunger, which slides along the inner peripheral wall surface of the cylinder hole (bore), is exposed from the cylinder hole (bore).
Therefore, even in the fuel pump of JPH04-231673A (corresponding to U.S. Pat. No. 5,174,734), similar to the high pressure fuel pump of JP2008-525713A, the exposed slide surface of the plunger may possibly be damaged by hitting, or a foreign object (e.g., debris) may possibly adhere to the exposed slide surface of the plunger, so that slide malfunction of the plunger may possibly occur.
Furthermore, in the fuel pump of JPH04-231673A (corresponding to U.S. Pat. No. 5,174,734), a size of the stopper structure, which limits the falling off of the plunger from the cylinder hole, is large. Also, this stopper structure is not formed to implement separation between a fuel range and an engine oil range in a case where the fuel range is provided at the lower end of the plunger although this depends on the intended use of the fuel pump.